Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
A photovoltaic (PV) array is a linked collection of solar panels. Most PV arrays use an inverter to convert direct current (DC) power produced by the solar panels into alternating current (AC) power. The panels in a PV array are usually connected in series, as strings, to obtain a desired voltage. A plurality of individual strings is then typically connected in parallel to increase current production.
In conventional PV power generation systems, there is a tradeoff between local power generation and system efficiency. Conventional PV systems do not support local control of PV panels. As shown in FIG. 1, a conventional PV system 100 typically includes a plurality of PV panels 102 connected electrically in series to form a PV string 104, and a single large inverter 106 processes power from the entire PV series string 104 for delivery to a load or a power grid 108. In this arrangement, if one or more of PV panels 102 are shaded or otherwise environmentally compromised, power production is reduced for the entire string 104. PV panel manufacturers have added reverse diodes to partially mitigate electrical impacts of local shading, soilin, or similar problems.
As known to one of ordinary skill in the art, simultaneously operating each individual PV panel 102 of PV string 104 close to or at its potential maximum power production level, termed a maximum power point (MPP), as enabled by on-going environmental conditions, has proven to be hard, even impossible, to attain. It is well established that this inability to operate individual PV panels 102 at their corresponding MPPs sacrifices power production. Power reduction can be 20% or more if PV system 100 is subject to local shading, and can be of the order of several percents even when PV system 100 is uniformly illuminated.
A known improvement to the conventional PV system 100 provides local power processing on a per PV panel basis. For illustration purposes, FIGS. 2 and 3 show DC-DC versions 200 and 300 that provide series and parallel connected DC-DC converters 206 and 306, respectively. As shown in FIG. 2, DC-DC converters 206 are connected in series via their respective outputs, while each is also coupled to one of PV panels 208. As shown in FIG. 3, DC-DC converters 306 are connected in parallel via their respective outputs, while each is also coupled to one of PV panels 308. A DC-AC version 400, shown in FIG. 4, provides a direct coupling between a DC-AC inverter 406 and a PV panel power 408, without any DC-DC converters therebetween. Based on the literature, DC-AC version 400 has only been used commercially in a parallel arrangement (not shown) of the DC-AC inverters 406, although a series version (not shown) has been reported.
In each of DC-DC versions 200 and 300, a local DC-DC converter 206, 306 is connected to a respective PV panel 208 308, and to a DC-AC inverter 210, 310, for the delivery of power to a grid 212, 312. The DC-DC versions 200 and 300 sacrifice efficiency, since power needs be processed twice between each PV panel 208, 308 and the grid 200, 300. In AC version 400, a PV system, which includes a large number of PV panels 408, also needs to include a corresponding number of DC-AC inverters 406, each of which processes a power generated by the correspondingly connected PV panel 406, to grid 412. Based on the configurations of FIGS. 2-4, all of the generated power must be processed through local DC-DC converters 206, 306 and DC-AC inverters 406, which can lead to excessive power losses.